An autoimmune disease is a condition that results from a pathological immune reaction against an individual's own tissues. Examples of autoimmune diseases, in which the immune system attacks otherwise healthy tissue include multiple sclerosis (MS), autoimmune uveitis, myasthenia gravis (MG), psoriasis, and rheumatoid arthritis (RA).
Multiple sclerosis (MS) is a chronic, neurological, autoimmune, demyelinating disease. MS can cause blurred vision, unilateral vision loss (optic neuritis), loss of balance, poor coordination, slurred speech, tremors, numbness, extreme fatigue, changes in intellectual function (such as memory and concentration), muscular weakness, paresthesias, and blindness. Many subjects develop chronic progressive disabilities, but long periods of clinical stability may interrupt periods of deterioration. Neurological deficits may be permanent or evanescent. In the United States there are about 250,000 to 400,000 persons with MS, and every week about 200 new cases are diagnosed. Worldwide, MS may affect 2.5 million individuals. Because it is not contagious, which would require U.S. physicians to report new cases, and because symptoms can be difficult to detect, the incidence of disease is only estimated and the actual number of persons with MS could be much higher.
The pathology of MS is characterized by an abnormal immune response directed against the central nervous system. In particular, T-lymphocytes are activated against the myelin sheath of the central nervous system causing demyelination. In the demyelination process, myelin is destroyed and replaced by scars of hardened “sclerotic” tissue which is known as plaque. These lesions appear in scattered locations throughout the brain, optic nerve, and spinal cord. Demyelination interferes with conduction of nerve impulses, which produces the symptoms of multiple sclerosis. Most patients recover clinically from individual bouts of demyelination, producing the classic remitting and exacerbating course of the most common form of the disease known as relapsing-remitting multiple sclerosis.
The activation and proliferation of T-lymphocytes involves the secretion of autocrine growth factors, such as interleukin-2 (IL-2) and the concomitant expression of its receptor (IL-2R) on the surface of the lymphocytes. A resting T-lymphocyte does not express IL-2R, but once activated by the appropriate antigen the cell secretes IL-2, which stimulates the cells of the immune system and up-regulates the expression of IL-2R, thus causing lymphocyte proliferation. This upregulation is believed to be involved in the immunopathogenesis of multiple sclerosis.
Several treatment options exist for treating MS. Acute bouts of neurological dysfunction are often treated with short-term administration of corticosteroids such as methylprednisilone. Interferon beta has been approved by the FDA as a treatment of MS in the United States and it is typically administered chronically in the treatment of long-term disease. The interferons are a major class of cytokine that play a role in immune activation and modulation. The putative mechanism of interferon-beta includes the inhibition of T-lymphocyte proliferation; inhibiting blood-brain-barrier permeability and T-lymphocyte transmigration into the brain by interfering with cell adhesion; and the upregulation of anti-inflammatory cytokines.
The two types of interferon-beta that are approved in the United States for use in treating MS are interferon-beta 1a and interferon-beta 1b. An interferon-beta 1b known as BETASERON® was approved as a treatment for MS in 1993 and is marketed by Berlex Laboratories, Inc. An interferon-beta 1a known as AVONEX® was approved in 1996 and is marketed by Biogen, Inc. Another interferon-beta 1a was approved in 2002 and is known as REBIF®, marketed by Serono, Inc.
According to the manufacturer's prescribing information, AVONEX® (interferon-beta) has been demonstrated to decrease the number of gadolinium (Gd)-enhanced lesions in subjects who were administered the drug for two years by up to 13% and to improve approximately 22% of subjects' Expanded Disability Status Scale (EDSS) scores. According to Samkoff, Hosp. Phys., p. 21-7 (2002), REBIF® (interferon-beta) can reduce relapse rates in subjects taking the drug by 33%. According to the Physicians' Desk Reference (1996), BETASERON® (interferon-beta) has been demonstrated to reduce the exacerbation rate in subjects taking the drug by about 31%.
As can be seen, none of these drugs is highly effective in treating MS. In fact, a substantial number of individuals do not respond at all, or fail to respond over time, to interferon-beta therapy. Thus, there is an urgent need to develop more effective treatments for MS, as well as other autoimmune diseases.
IL-2R antagonists bind to the IL-2R on activated T-lymphocytes, which inhibits IL-2 from binding to the lymphocyte and thereby interferes with the IL-2 dependent proliferation of activated T-lymphocytes. One such IL-2R antagonist is known as anti-Tac, an antibody specific for the alpha chain (Tac) of the human IL-2R on activated T-lymphocytes. A particular anti-Tac antibody generically known as daclizumab is a recombinant humanized monoclonal antibody. U.S. Pat. No. 5,530,101 discloses a humanized immunoglobulin that specifically binds to a human interleukin-2 receptor. That patent is assigned to Protein Design Labs, which markets an anti-Tac pharmaceutical known as SMART®. Roche Pharmaceuticals also markets an anti-Tac pharmaceutical known as ZENAPAX® (daclizumab).
ZENAPAX® (daclizumab) is used as an immunosuppressant to inhibit allograft rejection. It is not known to be beneficial in treating MS. ZENAPAX® (daclizumab) has been shown to be effective in the treatment of human T-cell lymphotrophic virus type 1 associated myelopathy/topical spastic paraparesis (HAM/TSP). Lehky et al., Ann. Neuro., 44:942-947 (1998). ZENAPAX® (daclizumab) has also been reported as an immunosuppressive agent in the treatment of posterior uveitis. Nussenblatt et al., Proc. Natl. Acad. Sci., 96:7462-7466 (1999). Other anti-Tac agents include basiliximab (SIMULECT®), BT563 (see Baan et al., Transplant. Proc., 33:224-2246 (2001)), and 7G8. Basiliximab has been reported to be beneficial in preventing allograft rejection, Kahan et al., Transplantation, 67:276-84 (1999), and treating psoriasis, Owen & Harrison, Clin. Exp. Dermatol., 25:195-7 (2000). Mig beta-2 is another IL-2R antagonist, but it is specific for the beta chain of human IL-2R.
In spite of these prior therapies, the search for a more effective treatment for MS has continued. Any treatment that could delay the progression or recurrence of the disease would be enormously beneficial to people who have this disease, by reducing neurological impairment and disability. Such a treatment could also reduce health care costs, by minimizing the amount of care patients require for their MS-induced neurological disabilities.